1. Field of the Invention
The present invention relates to methods and apparatus for inhibiting oxygen, moisture, and other gas or liquid penetration, and subsequent degradation of a device mounted on or protected by a flexible substrate. Examples of this device include a light-emitting device (e.g., organic light emitting diode (OLED) device), a display device, an electronic device (e.g., organic semiconducting devices), a photovoltaic device, a thin-film sensor, an evanescent waveguide sensor, a food container, a medicine container, etc.
2. Description of Related Art
Transport of oxygen or water through laminated or encapsulated materials and subsequent attack of an inner material(s) represent two of the more common degradation mechanisms associated with many devices, for example, light-emitting devices (OLED devices), thin-film sensors, and evanescent waveguide sensors. For a detailed discussion about the problems associated with oxygen and water penetration into the inner layers (cathode and electro-luminescent materials) of OLED and other devices, reference is made to the following documents: Aziz, H., Popovic, Z. D., Hu, N. X., Hor, A. H., and Xu, G. “Degradation Mechanism of Small Molecule-Based Organic Light-Emitting Devices”, Science, 283, pp. 1900-1902, (1999); Burrows, P. E., Bulovic., V., Forrest, S. R., Sapochak, L. S., McCarty, D. M., Thompson, M. E. “Reliability and Degradation of Organic Light Emitting Devices”, Applied Physics Letters, 65(23), pp. 2922-2924; and Chatham, H., “Review: Oxygen Diffusion Barrier Properties of Transparent Oxide Coatings on Polymeric Substrates”, Surfaces and Coating Technology, 78, pp. 1-9, (1996).
Unless something is done to minimize the penetration of oxygen or water into OLED devices, the lifetimes would be severely affected. Much effort has been expended to drive OLED operation towards 40 kilo-hour lifetimes, the levels generally regarded as necessary so OLED devices can overtake older display technologies as discussed in the following document: Forsythe, Eric, W., “Operation of Organic-Based Light-Emitting Devices, in Society for Information Display (SID)” 40th anniversary Seminar Lecture Notes, Vol. 1, Seminar M5, Hynes Convention Center, Boston, Mass., May 20 and 24, (2002).
The more prominent efforts to extend the lifetime of OLED devices include gettering, encapsulation and extensive device sealing techniques. Today one common way for sealing an OLED device is to use different types of epoxies, inorganic materials and/or organic materials that form a seal after they are cured by ultra-violet light, or heated by various means. For example, Vitex Systems, San Jose, Calif., www.vitexsys.com manufactures and offers for sale a coating under the brand name of Barix™ which is a composite based approach where alternate layers of inorganic materials and organic materials are used to seal the entire surface of the OLED device. Although these types of seals provide some level of hermetic behavior, they can be very expensive and there are many instances in which they have failed to prevent the diffusion of oxygen and water into the OLED device under prolonged operation.
The same sort of oxygen and water penetration problem is common in other types of devices as well as, for example, thin-film sensors, evanescent waveguide sensors, food containers and medicine containers. Accordingly, there is a need to inhibit the penetration of oxygen and water into devices, for example, OLED devices, thin-film sensors, evanescent waveguide sensors, food containers and medicine containers. Besides oxygen and water, other gas or liquid materials passing through the substrate material is undesirable. For example; organic solvents contacting a fabricated OLED device can destroy performance, and maintaining the carbon dioxide content of food products may be desired. This need and other needs are satisfied by the present invention.
The problems associated with oxygen and water penetration can be exacerbated when the device(s) are mounted on or protected by a flexible substrate as the mechanism for providing a barrier to the oxygen and water must withstand the mechanical stresses associated with the use of a flexible substrate.